The present invention relates to Radio Frequency identification (REID) systems and, more particularly, to a thin RFID tag which is printed on a thin flexible label and to methods of communicating with a thin REID tag.
Radio Frequency identification (REID) is a method of storing and remotely retrieving data using devices called REID tags. An RFID tag is a small object that can be attached to a product, animal, or person. REID tags receive and respond to radio-frequency queries from an REID reader. REID tags can be either active or passive. Passive tags operate by backscattering RF power and do not require an internal power source. Active RFID tags have an internal power source, e.g. battery, and typically have longer range and larger memories than passive tags. An active tag does not use backscattering of incident RF but includes a transmitter which transmits an RE signal to the reader. Active tags have numerous advantages over passive tags, however the cost of active tags is substantially higher.
An active tag, often used for real time location systems, includes an RE transmitter without a receiver and the active tag is programmed to transmit a tag identifier (ID) and optionally other pre-assigned or sensory data periodically at predetermined times. A more advanced type of active tag includes both receive and transmit circuitry which allow for both reading and writing data to the tag. A query is received by the mobile tag and the tag responds with data. The data is received by the REID reader and processed according to the needs of a particular application. The data transmitted by the tag may provide identification or location information, or specifics about the product tagged, such as price, color, date of purchase and other parameters.
The present invention utilizes in some embodiments inlaying of circuits and antenna in flexible materials to form an RFID label. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,951,596, all of which this application incorporates by reference for all purposes as if fully set forth herein.
Ultra-Wideband (UWB) communication, as approved by the US Federal Communications Commission (FCC) in February 2002, is a candidate for active tag RFID communication. Systems employing UWB typically employ an “impulse radio” or other wide-band methods for communicating the data, using low power transmission at RE frequencies between 3.1 Ghz to 10.6 Ghz, with bandwidth of at least 20% of the center frequency or at least 500 Mhz. An RFID system which includes a tag with ultra-wide band transmit and receive circuitry has been disclosed for performing distance measurements (e.g. over tens of meters) between a tag and a reader and/or distance measurements between different tags. PCT International Patent Application Publication No. WO 2003/098528, (PCT Patent Application No. PCT/IL2003/00358), by an inventor of the present invention, entitled “Method and system for distance determination of RF tags” and application PCT/IL2005/00506 are incorporated by reference for all purposes as if fully set forth herein. PCT/IL2003/00358 discloses an RFID system having the capability of automatically identifying unknown tags by sending a broadcast interrogation wide-band message signal and receiving responses from many (preferably all) tags that receive the message signal.
U.S. Pat. No. 6,002,708 entitled “Spread spectrum localizer”, which also discloses a method of distance determination by a wide-band system, is incorporated herein by reference for all purposes as if fully set forth herein.
Reference is now made to FIG. 2, which illustrates a prior art wide-band system transmission format as used PCT/IL03/00358. A transmission waveform is shown of short pulse bursts 20, or short pulse sequences 20. The total interval of bursts 20 is on the order of T1=100 nanoseconds, with a nominal time separation of symbol time Ts 22 between bursts 20 typically between 1 microseconds and 30 microseconds. Waveforms 20 can be employed for impulse radio with low power consumption implementations. Some systems include a sequence of known symbols at the beginning or end of a set of data. The known sequence at the beginning or end is called a preamble or postamble, respectively. A typical packet 20 includes a relatively long preamble which consists of known pulse sequences with no data modulation imposed and after the preamble is a packet delimiter and data. A ‘response’ period (or postamble) follows the data, to accurately time the response.
Reference is now made to FIG. 1, which illustrates a structure of a rigid-structured ultra wide band tag 10 of the prior art. UWB tag 10 is implemented on printed circuit boards 11 and 12. Antenna 15 is typically printed e.g. a bow-tie etched in PCB 11. Typically, a layer of first PCB 12 serves as a ground plane 16 of antenna 15 in order to achieve a wide bandwidth, as required in UWB communications, and reduced vulnerability to nearby materials. Ground plane 16 is separated by about a quarter wavelength (λ/4 where K is the RF wavelength) from the radiating part of antenna 15. The quarter wavelength is typically several mm, at radio frequencies of interest. Antenna 15, lithium coin battery 14, and crystal 13 lead to a thickness of tag 10 on the order of 1 centimeter. Tag 10 includes electronic circuitry, e.g. single communications chip, band-pass filter, crystal 13 and capacitor, all assembled on printed circuit board PCB 12. In some prior art tags 10, instead of a single chip, a communications circuit is implemented with several discrete parts. Crystal 13 is used as an accurate frequency reference to provide a clock source for timing and for generating the RF frequency of transmission and reception. A relatively large form factor, rigid structure and high base cost are among shortcomings of conventional UWB tags 10.
Smart active labels are thin (˜1 mm) and flexible devices that include an integrated circuit and a power source printed on the label, without a crystal reference. Printed batteries are in commercial use from several companies e.g. Power Paper Ltd. (Petah Tikva, Israel) and Solicore Inc. (Lakeland, Fla. USA). Currently, printed batteries have a low capacity compared with lithium coin batteries. Capacity for printed batteries is typically 20 mAh per square inch. US patent publication 20020192542 assigned to Power Paper Ltd. entitled “Flexible thin layer electrochemical cell and manufacturing of same” as disclosed by S. Luski and Z. Nizan and patent application publication 20050239917 assigned to Solicore Inc. entitled, “Lithium inks and electrodes and batteries made therefrom” as disclosed by C. R. Nelson et al. are incorporated herein by reference for all purposes as if fully set forth herein.
Smart active labels use back-scattering to transmit data, in response to a query signal from a reader or ‘interrogator’. In U.S. Pat. No. 6,888,509 entitled “Tamper indicating radio frequency identification label” disclosed by Atherton, a passive tag in the form of a label is described and a method is presented which alters the RFID signature if a label has been tampered. In US patent application 20040200061, entitled “Conductive pattern and method of making” disclosed by Coleman et al., a method is described for creating an electrically conductive pattern, applicable for producing an antenna on a label. In U.S. Pat. No. 6,700,491, entitled “Radio frequency identification tag with thin-film battery for antenna”, a passive tag is disclosed with one arm of a thin-film battery serving as a dipole antenna. In U.S. Pat. No. 6,087,996, entitled “Thin-film antenna device for use with remote vehicle starting systems” as disclosed by Dery, includes a flat antenna which attaches to a car window with a simple connection to a receiver. In U.S. Pat. No. 5,567,537, entitled “Magnetic core element for antenna, thin-film antenna, and card equipped with thin-film antenna”, a thin antenna is disclosed for thin PC cards with a low frequency range. In U.S. Pat. No. 6,940,408, “REID device and method of forming”, a method is disclosed by Ferguson et al. which improves the connection of an RFID chip with a label antenna, and an RFID inlay which includes conductive bumps or traces that electrically couple by strapping leads to the antenna. U.S. Pat. No. 6,940,408 also references other prior art including methods of producing labels. In U.S. Pat. No. 6,914,562, entitled “RFID tag using a surface insensitive antenna structure”, an RFID tag or label, as disclosed by I. J. Foster, is insensitive to or compensates for the substrate material of the tagged object. The antenna, according to U.S. Pat. No. 6,914,562, requires a ground plane of relatively large dimensions. In U.S. Pat. No. 6,914,573, “Electrically small planar UWB antenna apparatus and related system” McCorkle discloses a planar multi-layered wide band antenna that has a single-ended feed.
A thin and flexible UWB antenna may be produced. A representative reference in the area of UWB antennae include S. I. Latif, L. Shafai, and S. K. Sharina, “Bandwidth Enhancement and Size Reduction of Microstrip Slot Antennas”, IEEE Trans. Antennas and Propagation, Vol. 53, No. 3, March 2005, pp. 994-1004. Another design based on a specific form of patch on a partial ground is found in Choi, J. K. Park, S. K. Kim, and J. Y. Park, “A New Ultra-Wideband Antenna for UWB Applications”, Microwave and Optical Technology Letters, Vol. 40, No. 5, March 2004, pp. 399-402. IEEE Trans. Antennas and Propagation, Vol. 53, No. 3, March 2005, pp 994-1004 and Microwave and Optical Technology Letters, Vol. 40, No. 5, March 2004, pp. 399-402 are included herein by reference for all purposes as if fully set forth herein.
There is thus a need for, and it would be highly advantageous to have an active tag with a small form factor which may be printed on a flexible label and in particular a method for UWB communications with a small form factor which does not require a crystal for a clock and frequency source. A crystal is not desired since the crystal can not be printed nor flexibly attached on a thin label.